Amelogenesis imperfecta is a genetic disorder affecting the formation of enamel. The disease is both genetically and clinically heterogeneous. Genetically, there are X-linked, autosomal recessive and autosomal dominant forms of the disease. Recently, three Swedish families with autosomal dominant amelogenesis imperfecta (of the local hypoplastic form) have been used to localize a gene for this disease to the long arm of human chromosome 4 (Forsman et al., 1994). This region of human chromosome 4 appears to code for a number of genes that play a major role in tooth development. In addition to autosomal dominant amelogenesis imperfecta, this region also contains the locus for dentinogenesis imperfecta type II (DGI-II), a dental disorder resulting from abnormal dentin production Thus, this region is of major biological interest with respect to tooth development. Amelogenesis imperfecta is presumable a disorder of the ameloblasts, since these cells are primarily responsible for the production of enamel. A new cDNA uniquely coded by ameloblasts has recently been isolated. This cDNA codes for the protein termed "ameloblastin." Preliminary evidence supports the localization of the gene for ameloblastin to human chromosome 4. This proposal is based on the hypothesis that the gene for ameloblastin is responsible for autosomal dominant amelogenesis imperfecta of the hypoplastic type. To test this hypothesis we propose the following Specific Aims: 1. Isolate genomic sequences for the human ameloblastin gene. 2. Regionally localize ameloblastin on human chromosome 4 using fluorescence in situ hybridization. 3. If the ameloblastin gene lies in the candidate region, develop a new genetic marker(s) tightly linked to the gene and use this to analyze the amelogenesis imperfecta families. If tightly linked, screen the affected families for mutations. The long term goal of this project is to identify a gene causing an autosomal dominant form of amelogenesis imperfecta which maps to human chromosome 4. Then, this gene will be used to elucidating the biological processes responsible for normal enamel production. These preliminary experiments will be used to apply for a larger grant which will involve the use of genetic technique to study dental disease.